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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 32 |
| 5 | 180 |
| 6 | 954 |
| 7 | 6524 |
| 8 | 45016 |
| 9 | 360144 |
| 10 | 3023640 |
| 11 | 27617832 |
| 12 | 271481880 |
| 13 | 2775329232 |
| 14 | 31188079272 |
| 15 | 350827041000 |
| 16 | 4441125248640 |
| 17 | 54110311240512 |
| 18 | 765546040603584 |
| 19 | 9938498593229568 |
| 20 | 156934910753107200 |
| 21 | 2128783325724881280 |
| 22 | 37775147271084647424 |
[1,1,2,9,32,180,954,6524,45016,360144,3023640, 27617832,271481880,2775329232,31188079272, 350827041000,4441125248640,54110311240512, 765546040603584,9938498593229568, 156934910753107200,2128783325724881280, 37775147271084647424] |